1. Field of the Invention
The present invention relates to a method of manufacturing a magnetoresistive element having such a structure that a current is supplied in a direction perpendicular to the film plane, a magnetoresistive element manufactured by the method, a magnetic head assembly using the magnetoresistive element and magnetic recording apparatus using the magnetic head assembly.
2. Description of the Related Art
The performance of magnetic devices has been drastically improved by finding of the giant magnetoresistive effect (GMR) in a stacked structure of magnetic materials. In particular, since a spin-valve film (SV film) has a structure easily applicable to magnetic devices and efficiently exhibits the GMR effect, it has brought about marked technical improvement in the magnetic devices such as magnetic head assemblies and magnetic random access memories (MRAMs).
The “spin-valve film” has a structure in which a nonmagnetic metal spacer layer is sandwiched between two ferromagnetic layers. In the spin-valve film, the magnetization of one ferromagnetic layer (referred to as a “pinned layer” or “magnetization pinned layer”) is pinned by an anti-ferromagnetic layer or the like, whereas the magnetization of the other ferromagnetic layer (referred to as a “free layer” or “magnetization free layer”) is made rotatable in accordance with an external magnetic field. In the spin-valve film, a giant magnetoresistance change can be produced by a change of the relative angle between the magnetization directions of the pinned layer and the free layer.
Conventional spin-valve films are CIP (current-in-plane)-GMR element in which a sense current is supplied in parallel to the film plane. In recent years, TMR (tunneling magnetoresistance) elements and CPP (current-perpendicular-to-plane)-GMR elements, in which a sense current is supplied in a direction substantially perpendicular to the film plane, attract a great deal of attention because they exhibit a higher MR ratio than the CIP-GMR element.
On the other hand, there has been observed that a nanocontact between Ni wires exhibits a magnetoresistance effect with a high magnetoresistance change. See, Phys. Rev. Lett., 82, 2923 (1999).
Further, development of a magnetoresistive element in which the magnetic nanocontact is extended to a three-dimensional structure has been advanced. See, JP-A 2003-204095 (KOKAI). JP-A 2003-204095 (KOKAI) discloses, as a method of fabricating a nanocontact, more specifically as a method of forming a hole for the nanocontact, an electron beam (EB) irradiation process, a focused ion beam (FIB) irradiation process, atomic force microscope (AFM) technology and the like.
It is conceivable that the novel magnetoresistive effect described in the above documents may be derived from abrupt change of magnetization at the magnetic nanocontact. The abrupt change of magnetization at the magnetic nanocontact depends on a domain wall thickness or a domain wall width produced at the magnetic nanocontact. In other words, the abrupt change can be provided as the domain wall width is made narrower. In addition, since the domain wall width depends on a size of the magnetic nanocontact, it is preferable that the magnetic nanocontact has a small size. Further, it is preferable that the magnetic nanocontact or the domain wall has high purity of magnetic element. However, it is very difficult to form a magnetic nanocontact with a small size and high purity.